The present invention relates to a photoresist cleaning composition used in photolithography for stripping a thick photoresist pattern, and a method for treating a substrate therewith. The photoresist cleaning composition of the invention is suitably applied especially for the formation of a bump or pillar or redistribution layer (RDL) in the production of a semiconductor device, such as IC and LSI. It may also be used after an etch process, such as a Bosch etch process, in the formation of Through Silicon Vias (TSVs) on a silicon or glass substrate in the production of a semiconductor device, such as IC and LSI.
In recent years, with the high integration of semiconductor devices such as IC and LSI and downsizing of chip size, it has been required to reduce the size of the metallic wirings and to align bumps or pillars as connection terminals (minute salient electrodes) having a height of 20 μm or more on a substrate with high precision. In the future, with further downsizing of chip size, high precision of metallic wirings and bumps will become even more necessary.
The bump formation is carried out by, for example, providing a metallic thin film on a substrate, forming a thick photoresist pattern on the metallic thin film by photolithography technique, providing a conductive layer on the photoresist pattern-uncovered area (i.e., a metallic thin film-exposed area) of the substrate to form bumps, pillars or RDLs and then removing the photoresist pattern.
The photoresist pattern may be a thick film, usually in a film thickness of about 3-150 μm, and the photoresist may be a positive-working photoresist material since many common stripping chemicals for negative-working photoresists can severely etch or damage substrate materials such as copper, nickel, alloys of copper or nickel with various metals, Tin-Silver alloys (also known as SAC of varying compositions), TiN or other passivation materials such as SiN, polyimide, BCB, etc.
Since the photoresist pattern may be thick, usually in a film thickness of about 3-150 μm, the photoresist may be a negative-working photoresist materials in view of resistance to plating, pattern shape property, etc. It is typically more difficult to remove photoresist patterns made of the negative-working photoresist materials as compared to those made of positive-working photoresist materials, and therefore, it is even more difficult to remove thick photoresist patterns made of the negative-working photoresist materials relative to thick positive-working photoresist materials.
Further, the thick photoresist pattern may deform or collapse during the formation process, because of its heavy film thickness. In such a case, it is necessary to discontinue the subsequent process and to carry out a re-work by totally removing the deformed photoresist pattern from the substrate and repeat the steps used to form the photoresist pattern.
The removal of the photoresist pattern after the bump formation or the removal of the photoresist pattern for the re-work, typically takes place in a tank of a photoresist cleaning composition to strip away the photoresist pattern (cured material) rapidly and completely. It is important that the photoresist cleaning composition not corrode the metallic thin film while cleaning the photoresist, but it is important to remove the photoresist completely. In addition, in forming a bump on the substrate, a degenerated film is possibly formed at the interface between the photoresist pattern and the bump. It is therefore necessary to prevent corrosion of the metallic film and to protect the bump from corrosion or any other materials present that are not intended to be removed by the photoresist cleaning composition.
JP-A-08-301911 describes a radiation-sensitive resin composition as a pattern forming material for the use of a bump formation and discloses in paragraph Nos. [0032] and [0043] a mixture of a quaternary ammonium, dimethyl sulfoxide and water (specifically, a dimethyl sulfoxide solution of 0.5 mass % of tetramethylammonium hydroxide (containing 1.5 mass % of water)) as a stripping liquid for stripping a photo-cured pattern. However, this stripping liquid involves problems such that it takes time to dissolve the photo-cured pattern that was stripped away from the substrate in the stripping liquid, and that the throughput is low. Also, this stripping liquid causes high etching of various metal substrates used in these applications.
JP-A-10-239865 describes a formulation containing specific amounts of dimethyl sulfoxide, 1,3-dimethyl-2-imidazolidinone, a tetraalkylammonium hydroxide, and water as a stripping liquid for stripping a negative-working photoresist for forming a bump. As is the case of JP-A-08-301911 above, JP-A-10-239865 also involves problems such that it takes a time to dissolve the photo-cured pattern that was stripped away from the substrate in the stripping liquid, and that the throughput is low. Also importantly, this stripping liquid causes high etching of various metal substrates used in these applications. Further, the stripping solution in JP-A-10-239865 contains 1,3-dimethyl-2-imidazolidinone as an essential component. This compound causes discoloration or corrosion of Cu.
In the photolithographic field, JP-A-2001-324823, JP-A-07-028254, etc., disclose stripping liquids containing a quaternary ammonium hydroxide and a water-soluble organic solvent such as dimethyl sulfoxide. However, none of those describe at all the removability of the difficult to remove thick positive or negative-working photoresists that are suitably used for forming a thick pattern for the formation of a bump.
Other known compositions may strip away the photoresist, but also corrode the metals and other materials present on the substrates to be cleaned. A composition is needed that cleans well and results in little or no corrosion of the metal and/or passivation materials on the substrate.